JP 2011-256730 A discloses a manufacturing method for an engine. The method comprising the steps of; casting a cylinder head material having a recessed portion which forms a part of a combustion chamber, cutting a matching surface of the cylinder head material with a cylinder brook, measuring the distance in the height direction from a reference surface on a top portion of the recessed portion to the matching surface, and adjusting a cutting amount of the surface of the recessed portion based on the distance in the height direction. When the distance in the height direction is measured, an error with respect to the standard of the volume of the combustion chamber can be calculated. Therefore, according to the method mentioned above, the volume of the combustion chamber can be kept within a specified range.
Meanwhile, in order to improve a performance of an engine, a heat shielding film may be formed on a ceiling surface of the combustion chamber such as the surface of the recessed portion. When such heat shielding film is formed on the ceiling surface, it is possible to improve a performance of suppressing heat (i.e. heat shielding performance) generated in the combustion chamber from radiating to outside via the ceiling surface. In this case, however, the volume of the combustion chamber is decreased in accordance with that of the heat shielding film. However, forming the heat shielding film on the ceiling surface is equivalent to forming the heat shielding film after the cutting step of the ceiling surface is completed. Therefore, it is practically difficult to cut the ceiling surface after the heat shielding film is formed.
Instead of cutting the ceiling surface, a surface of the heat shielding film may be cut after the heat shielding film is formed. However, the film thickness of the heat shielding film has a high correlation with the heat shielding performance mentioned above. Therefore, when it is not enough to cut the surface of the heat insulating film and when the thickness of the film is highly reduced by adjusting the cutting amount of the heat insulating film based on the distance in the height direction, there is a possibility that a desired heat shielding performance of the film cannot be exhibited.
The present disclosure addresses the above problem, and an object of the present disclosure is to provide a manufacturing method of an engine capable of avoiding unnecessary cutting work of a surface of a heat insulating film which is formed on a ceiling surface of a combustion chamber within a surface of a cylinder head, and keeping a volume of the combustion chamber within a specified range.